Radiosignaling



. 1,668,270 J. F. FARRINGTON RADIOSIGNALING f *s Filed Nav. 2o. 1922 UPP/P55555 s, w/TH OR w/THOUT f3 JUPPREsst-s s, w/ 7H by /wy Patented May 1, 1928.

UNITED. STATES JOHN F. FABINGTON, OF NEW YORK,

PANY, INCORPORATED,

N. Y., AssIGNon rro or NEW YORK, N,

wnsrnnnamcfrarc con- Y., A CORPORATION or `NEW Yonx.

MDIOSIGNALING.

Application led November 20, 1922. Serial No. 601,975.

rlhis invention relates to carrier wave signaling and particularly to repeating systems for amplifying at intermediate polnts the signal transmitted between two radio stations. V y

An object ofthe invention is to provide a system for two-way radio repeating, and

to prevent at the repeater station the `useless and l0 which attends tlie'condition 0f singing An additional `object is to provide a radio repeating system which is effectiveto preveut .singing the use'of` a single antenna-for transmitting and receiving or where physical conditions arev otherwise especially conducive to interference between the transmitting and re ceiving circuits.

A radio repeating station, in general, com prises an antenna structure for receiving a radio wavefrom a distant transmitting sta tion or from another repeating circuit, circuits for amplifying the received Wave, and an antenna. structure for radiating the amplified wave. Considerations of economy usually require thatthe two antennae be in close proximity or be combined in la unitary structure. In' either of these cases, a pote`ntial Lsinging circuit is provided by the 3u amplifying circuits andthe connection between the transmitting and receiving antennae which may, as in the former case, be an ether `link or, as in the latter case, a conductive connection. Singing occurs when the energy' loss through the closed singing circuit is exceededby the amplification.` Since singing is detrimental to a faithful repetition `of the signal at the repeater and must be avoided, the efficient use of the repeater, which obviously depends on the amplification' capable of being secured, is accordingly cal conditions imposed the circuits to sing.

Methodsfor increasing the effectiveness of the repeater stations been directed toward increasing the loss or attenuation `of the circulating energy in the singing circuit or, as explained in a different way, towards increasing the Vimpedance of the singing circuit to the circulatingcurrent. To this end the expedient has been used of directive transmission and reception at the'repeater. Electrical balance between the transmitting and receiving antenna'cir- Lili by the liability of wasteful circulation of energy under `conditions requiring tenna used 'in common limited by 'the criti have accordingly the `carrier wave during its cuits has sometimes been used, either' alone or supplementary to other means. A common expedient has been to change the requency of the received wave at somel point in itspassage through the repeater and to radiate it` at itschanged frequency. Since, in this arrangement, the receiving antenna is tuned to a frequency different from that transmitted from a repeater, it is incapable of efiicient reception thereof and the closed loop through whichsingingtends to occur is given such a high attenuation as to prevent singing. VVhere a commontransmitting and receiving antenna is used an effect analogous to that secured with a `two-an-` tenna arrangement may `be secured by inserting a trap or anti-resonant circuit in the receiving circuit tuned to the frequency of the transmitted wave.

In applicants invention, singing is prevented by changing the carrier frequency, but the circuits `for accomplishing thisV are quite diferentfrom those of the prior art. Considered broadly, applicants method involves the following sequence of operations. The incoming signal modulated Wave is combined with a wave from a local source to produce a difference frequency Wavemodulated in the same manner as the received Wave. This wave is detected to produce the signal component which is then used to modulate an outgoing wavehaving a frequency differing from that of the incoming wave, the resultant wave being transmitted either from an individual antenna or from an anfor transmitting and receiving. The outgoing Wave is preferably built up by first modulating an intermediate frequency wave with the signal and combining the resultant Wave with the Wave from a local source to produce-the sum` frequency component. The receivingand transmitting operations are accordingly quite similar to the methods of receiving and transmittin identified by the term successive detection and successivel modulation and have the usual advantages which attend the use of arrangements of these general types, namely, amplification and increased selectivity (and hence increased discrimination against Vatmospheric disturbances and against undesired signal waves). i y

Y By reason of the change of .frequency of passage through the repeater',` conditions are made unfavpr- 110 1 quency, resulting able to singing as in the other example pf A n Y this general type of repeater system. additional im ediment to singing which 1s not found in t e prior systems results on account of the particular type of receiving arrangement, since any combination frequency which would result from interaction of the received and transmitted waves maybe made different from the normal auxiliary frefrom the combination of the received wave with the wave from the local source, and accordingly, is ineliiciently transmitted by the receiver circuits which are tuned to the normal auxiliary carrier Wave.

In the preferred embodiment of the invention, a single local source'is used for the first step of detection and the linal step of modulation, that is, the wave from this source is combined with the normally received wave to produce a modulated auxiliary frequency carrier Waveand is itself modulated by a lower frequenc Wave which, in turn, is modulated t eV signal. The modulation of the outgoinfr wave effectively' increases its frequency by the signal modulated wave frequency. The singing circuit is accordingly given a high impedance lfor the circulating current by each of the two means described in connection with the general case, namely, by circuits capable of discriminating between the incoming and outgoing frequencies and by the auxiliary frequency tuning, which discriminates against the undesired combination frequency. The preferred arrangement is especially advantageous under unusual Yconditions of space limitation, since use may be made of the interference from the transmit-ting circuit to establish the auxiliary frequency wave. Ina practical case` this arrangement permits efficient repeater operation when a single antenna is used for transmitting and receiving, reliance being had principally on the effect of auxiliary frequency tuning to prevent singing.

It vshould be noted that the successive modulation method used at the repeater makes possible the effective use of the successive detection method at the terminal receiving station with its attendant advantages of increased amplilicationand selectivity, an important feature of applicants invention.

Among the further objects and features of the invention which will be apparent from the reading of the following description is that of providing efficient and simple forms of circuits for carrying the principles of the invention into effect.

In connection with the detailed description reference will be made to the accompanying drawings wherein Fig. l illustrates a Vpreferred form of the invention in which a single local source is used for the first step of detection and the final step of modulation,

2 illustrates a diete carrier frequency system similar to that of Fig. 1 but arranged for two-way operation and Fig. 3 illustrates the, terminal arrangement which may be used at a station designed to cooperate with the repeater of either Fig. 1 or Fig. 2.

In the description and drawing certain of the elements will, for convenience, be identified by reference letters which arev sugges-V tive of their functions elements of the same kind being distinguished from each other by subscripts. For example, the letters'D, M, A, and F will be used to represent respectively a detector, modulator, antenna, and filter. It will be assumed with respect to, each of the figures that it is desired to communicate between two stations sending out waves of frequency f, and 4, which will be assumed for convenience to erespectively 7 00,000 and 720,000 c cles. These waves are assumed to kbe mo ulated, respectivel by speech or other audible frequency signals S1 and 8,. Although a single repeating station will be assumed, the extension of the system so as to include any number of such stations will be obvious.

In the drawing, except Where otherwise indicated, the frequency labeling of the lilters refers to transmitted, rather than to suppressed frequencies. Asl will be explained later, these filters may be alternatively adapted for the transmission of various other combinations of frequencies than that indicated, each of which will, however, involve certain of the frequencies in the combination, actually indicated in the drawing and no additional frequencies produced in the system, i. e. such combinations will include merely a lesser number of the frequencies indicated. Frequency labels for these alternative combinations are not used since they would tend to greatly confuse the illustration of the invention.

VReferring to Fig. 1, which disclosesv circuits for one-way repeating from a station transmitting a frequency f, to a station transmitting frequency' f4, the antenna A with the branched circuit 5 and parallel circuits through 3 to ground constitutes, in combination with the reactance of the generator G, a lreceiving yconductor which is tuned to the incoming carrier frequency f1. The legend fliS, indicates that the received wave comprises the unmodulated co1n ponent f, and one or both of theside bands flJrS, and f,'-Sg,. In the anal "sis that follows it should be understood tiat this doule sign wherever occurrin signifies that either or both of the side liands indicated by the two signs may be present.

The local source G is used in the first `of the two steps of detection to ste down the received carrier frequency and 1n the final step of modulation to step up the intermeto the value required sov y mitting although a single antenna is shown.

iti

In order that theantenna may be doubly tuned so as to respond to the transmitted carrier frequency as well as to the receiving carrier fre uency the branched circuit 5 is made an e ectiveopen circuit for waves of the transmitted frequency by the insertion of the circuit 2, which is anti-resonant at the mean frequency of the transmitted carrier wave, the aerial portion of the antenna A with the transmitting circuits being tuned;y

to resonance at said frequency. Since the .c transmitted wave is a successively modulated wave of the radio carrier frequency f2 of thesource G modulated by a signal `modulated wave, the mean frequency of the transmitted wave would be f2 if both side bands of frequency f2 are transmitted. If a single side band is transmitted the antenna would be tuned to a frequency differing from f, by the mean signal modulating frequency. Al-

though circuit 2 is substantially anti-reso-` nant at frequency f, sufficient energy of that frequencys transferred to circuit 5 from generator' G to enable thegenerator to accomplish 'its function as a local receiver source. For this purpose circuit `2 may, if

necessary, be slightly detuned.` A separate transmitting antenna may be used if desired in which case the localenergy for reception may be transmitted tothereceiver circuit by radiation as is shown, for example, in U. S. patent to Farrington, 1,495,47 0, Ma 27, 1924. Frequency f2 may be higher or ower than f1. It is assumed to be 750,000 cycles.

Thereceived energy and the energy from the generator G is transmitted throughcircuit 4 or any other selective circuit to high frequency detector D. The circuit 4 is'adjusted to resonance with currents `of frequency f1. Thetuning of this circuit is sutilciently broad, however, to `permit a certain amount of current of'frequency f, 'to pass therethrough. Detector D and the other detectors to be described may each be of any of the types commonly used for operating on a high requency modulated wave'to produce the modulating component. A. vacuum tube detector is shown in each case.` The action of such a device in combining simultaneously impressed waves is explained in considerable detail in BritishPatent No. 102,503. Among components resulting from detection will be the lower sideV components having the difference frequencies f,- f1 and (fzf1) :tsp Assuming speech modulation, the essential speech frequencies being included in the range between200 and 2000 cycles, these component side bands would comprise respectively, frequencies from 48,000 to 49,800 Cycles and from 50,200 to 52,000 cycles. These components are selected and transmitted to auxiliary frequency detector D1 by a. band filter F which may be `of the type described in pages 312 to 314, inclusive, of a paperby Colpitts and Blackwell, Carrier Current Telephony and Telegraphy, vol. 40, No. 4 of the Proceedings of the Institute of Electrical Engineers. i

Detector D1, which may be similar in all respects tol D` operates upon the difference frequency waves selected 'by the band filter to give the signal frequency component S1. This signal component is selected by low pass filter F1, which cuts off at theupper limit of voice frequency, and impressed upon modulatorM to modulate intermediate carrier wave of frequency f3 supplied by a local source G1. If desired the modulator M may beof the well-known balanced type described inthe article (Carrier Current Telephony and Telegraphy) referred to above, inwhich modulation would be attende-dby elimination of the unmodulated component of frequency f3.

A band pass filter F2, which may be of the sametype as F, suppresses the signal component- S, and transmits to n'iodulator M1 either or both of the side bands )21231, in

either case with orwithout the uninodulated component of frequency 72,. Generator G supplies a wave offrequency f2 to modulator M1 which may beV of the type illustrated by M but is preferably of the constantcurrenttype described at page 300 of a papel' by Craft and Colpitts, Radio Telephony, volume 8, No. 3, Proceedings of American Institute of Electrical 'Engineers This final `step of modulation yields a successively modulated wave of radio carrier frequency f, and an intermediate carrier frequency f3. The repeating `operation accordingly is,`in effect, an amplification of the received wave and a retransmission with the new carrier frequency fgfa, or fftfa, the wave of this frequency being modulated by the signal S1. If a wave of frequency f, is impressed on modulator Ml the retransmitted wave contains the unmodulated component fzif, as well as the'side bands so that the signal S, may be detected at the terminal, or another repeating, station, by `a single detecting operation in the ordinary way. .In this case the unmodulated component f, would be of no use at the terminal station and, with one side band if desired, may be suppressed before transn'iission with conscquent economy of energy and frequency range. `In this case the unn'imlulatcd component may be supplied to lthe circuit 5 or 4"`by a direct connection to generator 'G through circuits A0 and 7, switch 8 being thrown to the left, or bya separate source 9 through circuit 7, the switch being thrown tothe right. If recourse is not had to these means for impressinga current directly on circuit l4, the switch is, of course, left in neutral position. In the alternative that the components necessary for detection of S'1 by a single operation are not present, or even if these components are present, detection f ly modulated wave will mean, consistently withthe above, that frequency which when combined with such successively modulated wave will yield the signal in one detecting step. In the case of a successively modulated wave produced by modulating an intermediate frequency wave by a signal wave,

` and modulating a high frequency wave by the resultant wave, the carrienwave will have a frequency equal to the sum or difference of the frequencies of the high and intermediate frequency waves. lhether the sum or difference is taken will be indicated by the context.

In a system of the type described the combination frequency wave resulting from interaction in detector D of the wave transmitted from the repeater and the wave incoming from the distant station transmitting carrier frequency f1 would result in a spurious auxiliary frequency which would differ by f3 from the desired auxiliary frequency for which the auxiliary circuit including filter F is adjusted. Any portion of this wave transmitted through the filter after detection by D1 will give a component siS1 which will not pass filter Fl.- It is readily seen that f3 must be given a sufficiently high value so that faiSl can be separated from S1 by filters F1 and F2. f2 should have such a value that frequencies f2-f1 and f2-f1i S1 can be separated from S1. 5,000 cycles has been suggested as a practicable value for f3. It is to be noted that the successive'detection arrangement in this system makes possible the use of a smaller frequency difference ff: f3HV f1) between incoming and outgoing wave frequencies than is possible with syste-ms of the prior art on account of the increased discrimina-l quency for which F is adjusted and the spurious auxiliary frequency established by interaction of the transmitted and received waves and the difference betweenpthese two frequencies could be made much greaterthan Fig. 2 illustrates an application of the principle to two-way communication.l Assume thatin addition to the one-way communication of Fig. 1 there is an opposite communication from a station sendin out waves of a carrier frequency f4 and Signal frequency S4.

Vhen the two oppositely directed channels are simultaneously in operation, waves of frequencies f1, fliS1 and f4, ffiS4 are impressed on the receivin antenna of the repeater. The antenna circuit containing the generator G is tuned totransmit current ofr frequency f, and a side band of that frequency, while the branch circuit 5, together with the transmitter circuit is broadly tuned to frequencies f1 and f4.

Assuming f4 to be 7 20,000 cycles, detection by D will yield, among other components, the combination frequencies fz--f1 and fzand these frequencies modulated by their respective signals. With the values assumed these combination frequencies Will'have the values, respectively, of 50,000 and 30,000 cycles. The former with its si al side bands will be transmitted throng circuits F, D1, F1, M and F2 as in Fi 1. The latter with its side bands in a simi ar manner will f he transmitted through circuits F3, D2, F, M2 and F5. The'signal modulated intermediate carrier waves resulting` from the last modulating operation are impressed to` gether by circuit 1 on modulator M1. The transmitted wave from said modulator is a double modulated wave having two sets of intermediate carrier andsignal frequencies. If the values of the intermediate carrier frequencies f3 and f5 are properly selected, 5,000 and 10,000 cycles respectively, in the assumed case, the wave received at the terminal station can be ut through the detecting operation to be escribed and the signal components S1 and S4 se arated.

Although in the ease which the intermediate carrier frequencies are transmitted to M1, it is possible to produce a signal at the terminal station by a single detecting operation, the preferred arrangement involves the use of successive detection and, in particular, the triple detection arrangement of Fig. 3. The station of Fig. 3 transmits amodulated wave of carrier frequency f1, lto which the antenna A and transmitting circuits are tuned. The station receives two sets of double modulated waves Veach having the radio carrier frequency f2, and one havin an intermediate carrier frequency f, an signal frequency S4 and the other having the intermediate Vcarrier frequency f,.and signal frequency S1, Vthe latter being the wave originally transmitted from the station of Fig. 3 and retransmitted back to that station vfrom the repeater. Antenna and branched circuit 5 are tuned broadly to include these frequencies. 1f both side bands of f2 are transmitted, the frequencies will range between? 62,000 and 738,000fcycles.` It is entirely immaterial, so far as the receiving function is concerned, Whether one or both side bands,either of frequency f1 or of the intermediate carrier frequencies, are transmitted,

from the repeater.

The output of the detect-er1)3 Will have, among other components, difference frequencies having values of 50,000, 50,000 plus and minus 7,000 and 50,000 plus and minus 12,000 c cles, taking the maximum value of speech requencies assumed as representing all speech frequencies. Since it is desired to receive signal S4, filter F6. is designed to pass currents of 38,000 and 62,000 cycles or it may be designed to pass only one of the frequencies 38,000 or 62,000, if desired orif only one of such frequencies is transmitted to the terminal station. If only one'of these' frequencies 38,000 or 62,000 is transmitted, the filter can be designed to pass currents of frequencies between 58,000 and 62,000 cycles or, if a singlesignal bearing side band is used, it can be designed to pass currents of frequencies between 58,000 and 60,000 cycles or between 60,000 and 62,000 cycles and discrimination is secured at this point from the undesired intermediate frequency Wave modulated by signal S1. The product of the aux. f

iliary detection by D includes Waves of frequencies 10,000 t S, and 5,000 i Slif filter F,x passes both intermediate frequencies f, and f.,. In thiscase, the component 10,000 i S4 lis selected by'filter F, and the signal frequency S, is obtained from the output of the V10W frequency detector D5, after selection by filter Fs if desired. If the filter F, is designed to `suppress all components within the range 38,000 to 62,000 except a single unmodulated component such as 60,000 and accompanying side bands 60,000

l- S and 60,000 S, the undesiredfintermediate carrier, signal modulated, Wave, i. e. all frequencies Within the range 50,000 5,000 S and 50,000 -l- 5,000 l- S would be eliminated by filter F8 and the additional stages of selection, although preferably used, would notJ be necessary for discrimination from the other signal modulated, intermediate carrier, frequency. If current of frequency f5 is not transmitted from the repeater station as a modulation of f2, it must be supplied fromy a local source, as generator G4. If this component is transmitted the local source Gr,E may be omitted.

rThe result of the final stage of detection and the first stage of modulation both at the repeater may be considered a change in the auxiliary carrier frequency. It is obvious that an e uivalent change may be secured Without etection of the signal coin.-

ponent and the invention is to be understood as covering broadly any method or inl strumentality for accomplishing this change.

The novel features believed to be inherent in the invention are defined in the appended claims. i

What is claimed is:

`1. The method of radio repeating which comprises transmitting a carrier Wave, receiving a signal modulated radio Wave having a different frequency, combining a portion of the transmitted Wave With the 'received Wave to produce an auxiliary modulated carrier wave, select-ing said auxiliary modulated carrier Wave, changing the frequency of said auxiliary carrier Wave, and modulating the transmitted Wave with said changed frequency auxiliary modulatedy wave. i i

2. The method of radio repeating which comprises transmitting a carrier wave, receiving a signal modulated radio Wave having a different frequency, combining a portion of the transmitted Wave with the received Vwave to produce an auxiliary modulated carrier Wave, selecting said auxiliary modulated carrier Wave, detecting theA auxiliary modulated Wave to produce the signal Wave, modulating a sub-carrier wave with said signal Wave, suppressingy the signal component and modulating said transmitted Wave with the sub-carrier .modulated wave.

3. The method` of two-Way radio repeating which comprises transmitting ai carrier `wave, receiving a plurality` of modulated radio Waves having frequencies different' from eachother and from the frequency of the transmitted Wave, combining a portion of the transmitted wave with the received waves to produce a pluralityl of auxiliary carrier modulated waves, selecting and de-` tecting each of said auxiliary carrier Waves `to produce their respective modulating comsub-carrier or signal frequency waves will .give frequencies only without the signal frequency range.

4. A radio repeater comprising in com-` bination a receiving conductor resonant to the frequency of the incoming Wave, a local source, means for combining energy from the local source with the incoming Wave to pro-' duce an auxiliary frequency wave, selecting means for sa1d auxiliaryV frequency Wave, means for changing the frequency of the auxiliary frequency Wave, means for modulating a portion of the energy from said local modulating the wave from the sub-carrierV source with the detected modulating component, means for suppressing the unmod'ulated component, and means for selectively transmitting said sub-carrier modulated wave as modulations of a radio carrier wave,

the frequencies of the waves from said sources and of the transmitted Wave being so chosen that the sum of the frequencies of the radio 4and sub-carrier Wave is different from'that of: the received -wave and of such value that interaction withY the incoming wave will result only in Vcombination frequencies different from that for which said selective auxiliary Yfrequency circuit is adjusted.

6. A' radio repeater, comprising a receiving conductor` resonant to the frequency of an incoming modulated carrier Wave, a transmitting source, a transmitting conductor resonant to the wave from said transmitting source, means for combining a portion of the energy from said source with the received Wave to give an auxiliary frequency modulated carrier Wave, selecting and detecting means for said auxiliaryl frequency carrier modulated wave, a sub-carrier frequency source, means for modulating the wave from the sub-carrier source by the detected modulating component, and means for selectively transmitting, said sub-carrier modulated wave as modulations of the wave from said transmitting source, the frequencies of the waves from said sources being so chosen that the sum of the frequencies of the radio and.

sub-carrier Wave is different from that ofthe received Wave and of such value that interaction With the incoming wave will result only in combination frequencies different from that for which said selective auxiliary frequency circuit is adjusted.

7. The combination as defined in claim 6 in which the receiving and transmitting conductors are combined to Vform a single double tuned antenna for receiving and transmit-- ting,

resonant to the frequency of the incoming Wave, a local source, means for Vcombining energy from the local source with the incoming wave to produce an auxiliary frequency selecting means for said auxiliary frequency Wave, aV second circuit connected with the above mentioned circuit including'means for producing a wave, means for )modulating therewith; a portion of the energyfrom said local. source and means for transmitting said modulated wave. Y

y 9. The method of radio repeating which comprises generatin a wave, receiving a signal modulated ra io wave having a different frequency, combining a portion ofsaid generated wavewith the received Wave to produce an auxiliary modulated carrier Wave and utilizing said auxiliarymodulated carrier wave and said generated wave to produce a modulated carrier wave whose frequency is different from that of the generated wave, and transmitting said finally modulated wave.

JOHN FARRINGTON.

8. In combination a receiving conductorV eok AWave, a circuit connected thereto including a 

